How To Obtain Oil Samples

How To Collect a Proper Oil Sample From Transformers

Techniques That Yield Accurate Data

Trying to assess the condition of electric apparatus? Oil samples must be properly taken to minimize contamination: Only then can you obtain accurate data. These instructions are intended for use with bottles and syringes in obtaining reliable oil samples in order to determine dissolved gases (ASTM D 3612, IEC 60567), dissolved water (ASTM D 1533, IEC 60814), and other oil-quality tests.

The following techniques should be helpful in obtaining samples either through the drain valve equipped with the appropriate reducing fittings and hose barb (recommended) or through the small sampling port that's usually mounted on the side of the apparatus drain valve.

SAMPLING PROCEDURE

• The apparatus to be sampled must be under positive pressure.

• Clean the outside of the valve with a lint-free cloth.

• With the drain-valve plug removed, the valve through which the sample is to be taken should be thoroughly cleaned by whiping and then flushed, approximately 3 to 4 liters (quarts) of oil.

• With the plastic tubing connected to the drain valve or the small sampling port, adjust the valve for a gentle flow of oil through the tubing to minimize bubbles.

TAKE-AWAYS
Valve through which the sample is taken should be thoroughly flushed. Always clean the outside of the valve with a lint-free cloth. The main drain valve is recommended for taking samples. The handle of the plastic stopcock always points to the closed port leaving the other two ports in open communication.

BOTTLES

• Rinse each bottle 3 times (using the oil you will be sampling) with 1/3 of the volume of the bottle to prepare the bottle, then fill glass bottles (with tubing) touching the inner wall of bottle to minimize mixing of air to within 1 inch (2.54 cm) to the top and close the bottle. Plastic and metal bottles can be filled to overflowing and then capped.

SYRINGES

• Connect the syringe to the tubing with the syringe stopcock open. This is to permit flushing of the stopcock (handle toward the syringe). NOTE: The handle of the plastic stopcock always points to the closed port leaving the other two ports in open communication. Make sure the syringe stopcock is firmly seated on the syringe before taking the sample.

• Turn the stopcock slowly to the open position (handle in line with the flushing port) and allow 30 to 40 cc (mL) of oil to enter the syringe. Immediately close the stopcock (handle toward the plastic tube) and turn the syringe in the vertical position.

• With the syringe vertical (stopcock up, handle away from the syringe), eject any air bubbles and carefully depress the syringe piston until all of the oil has been ejected from the syringe.

• Close the stopcock (handle toward the flushing port) and repeat this flushing procedure 2 to 3 more times before taking the actual sample.

• To take the actual sample, open the stopcock (handle in line with flushing port) and allow oil pressure to push the piston back until the syringe is filled to approximately the 40-cc mark. Do not pull the piston manually since this can result in bubble formation. 50-cc syringes should be filled to approximately the 40-cc mark. 30-cc syringes should be filled to approximately the 25-cc mark.

• Close the stopcock and separate it from the tubing and inspect for air bubbles. If air is present, discharge the air immediately with the syringe vertical (stopcock up) and then close. It there are more than just a few air bubbles, empty the syringe and repeat the process until a proper sample has been taken. The filled syringe should contain no air, should be protected from light and packaged immediately. Bubbles may form after sampling, but do not attempt to remove these bubbles, as they are part of the sample.

• Fill out the Sample Identification information on the front of this form and return with the samples. Make sure to include the top oil temperature at the time of sampling.

	RESOURCE KIT			Ensure accurate oil samples with the Doble Porta Sampler. The Doble Porta Sampler can be used to: tell when the valve has been adequately flushed determine the water content of the oil.
	For more information on oil sampling For more information on test equipment

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